This invention relates generally to rotor blades for turbine engines, and more particularly to improvements in tip cap configurations for hollow, air cooled turbine rotor blades and method of fabrication thereof.
In the operation of a turbine engine, energy in the form of flow velocity of gaseous reaction products from the combustion chamber of the engine is used to drive the rotor of the turbine by passing the gaseous products against a plurality of turbine blades mounted on the turbine rotor and disposed in the path of the gaseous flow. The temperature of the gaseous combustion reaction products contacting the rotor blades of the turbine is ordinarily in excess of about 2500.degree. F., and engine performance may be optimized in many applications by allowing a high operating temperature for the turbine inlet. In order to provide turbine rotor blades which can withstand these temperatures, it has been found desirable to provide hollow turbine blades which may be cooled by flowing air through the blades. To this end, existing turbine blade configurations have included hollow castings having internal air conducting chambers or passageways having suitable inlets and outlets through which coolant air may be passed. Existing methods for casting hollow rotor blades suitable for turbine blade application, however, ordinarily result in a cast blade which has an open tip end characteristic of the casting process. The blade thus must be provided with a suitable tip end closure to distribute air flow throughout the blade.
Existing tip cap configurations include the one-piece type as disclosed by or referenced in U.S. Pat. No. 3,899,267. This configuration comprises a one-piece tip cap having peripheral impingement cooling holes, and held in place mechanically by peripheral crimping of the blade tip and by brazing. This configuration provides suitable cooling to the blade and tip, but the crimping operation may be unreliable and may be characterized by an undesirably high fabrication reject rate. A two-piece cap configuration such as that described in U.S. Pat. No. 3,982,851 and U.S. Pat. No. 4,010,531 comprises two individual cap portions per blade which have peripheral impingement cooling holes, the cap portions being held in the rotor blade tip by retaining lugs in the blade casting and by brazing. The midchord area of the blade tip of this configuration may receive insufficient cooling which may result in severe distress in the tip area.
The present invention provides a rotor blade tip cap assembly comprising a plurality of layers attached to the tip end of the rotor blade casting, each layer having a plurality of peripheral holes which communicate with each other in the assembled state and with the air passageway internal of the blade casting to define a plurality of outwardly opening torturous, serpentine-shaped coolant passages in the periphery of the assembled tip. A high pressure turbine rotor blade fabricated according to the present invention is characterized by highly efficient cooling capability, minimal thermally induced low cycle fatigue, excellent oxidation resistance, low fabrication costs, and simplicity of manufacture and repair.
It is, accordingly, an object of the present invention to provide an improved turbine rotor blade.
It is a further object of the present invention to provide an efficient and economical tip cap closure for a hollow turbine blade.
These and other objects of the present invention, along with the attendant advantages, will become apparent as the detailed description of certain representative embodiments thereof proceeds.